I tend to field three hastati, two principes, three triarii in a 3-2-3 "deformed quincunx pattern" as the core of my line; I also tend to use my pila on autofire though - moving close/waiting for them to approach and then switching to autofire and then charging when the enemy is wavering a bit. I also use my leves forward - if I am fighting phalanx then I use them on the flanks to give enfilading fire, if I am fighting impetuous troops I use them in front to lure the enemy towards my main line to be cut up (or to lure them faraway if they are drapanai or gesatae so they get worn out and peppered with missiles until my cavalry can mop them up).

I don't use a lot of mercenaries, although I am planning on adding Gallic and Hellenic archers when I can (for the army and for wall defence) and I often find myself using Hellenic light cavalry mercenaries and trying to save my equites from casualties during multistage offensives.

Strategically, I find myself coming home to Rome more often than in earlier builds - Rome has a good population and those morale bonuses and I also think its sort of appropriate to try and winter my armies in my main cities from time to time.

The true weak spot for the Romans, for me, seems to be in archers for city defence. I feel a little "exposed" without a couple of large units of bow-armed chaps to chase away Gauls and door-to-door salesmen.

I also agree with SwordMaster if by enemy cavalry he means skirmishing missile cavalry - its a serious blind spot for the Romans with their limited cavalry and long range missile options, Carthaginian generals still seem pretty tough too, although they feel easier than they were in 0.7.2.